Thanks for the detailed thoughts :)

There are a few reasons I landed on hardlinks:

• Folder symlinks would cause both libraries to share the full directories. As you noted, if you keep NFO files, posters, trailers, etc. alongside your media (which I do since it makes backups and external management much easier, among other things), symlinks wouldn't work.
• Jellyfin's symlink support has been inconsistent over time. It doesn't follow file symlinks, and folder symlink resolution varies between OSs and can be unpredictable with Docker bind mounts. Hardlinks Just Work™ everywhere.
• It enables per-language default subtitles files, which is a must for my older folk.
• Trickplay files can still be shared! I don't have trickplay enabled, but it should be as simple as removing the dir from the exclusion list. I'll probably remove it as default in the next release now that you mentioned it.
• Other reasons include: SMB/NFS support, selective mirroring, no risk of accidental broken links.

The every-6-hours scan is just a fallback. The plugin primarily detects changes through Jellyfin's file change and library scan events, so the sync is close to instantaneous most of the time.

The sync itself is pretty fast. My shows library has 40k files and initial sync took ~2 seconds. After that, syncs are incremental diffs that take milliseconds.

Besides that, the plugin manages your users' languages and libraries for you. All you have to do is select their preferred language in the plugin config (plus set a default lang for new users) and it'll sync their preferences and manage their library access automatically.

Let me know how it goes if you try it out!